Fluidic thermoelectric generator

ABSTRACT

A thermoelectric generator that utilizes the high temperature generated by fluid compression waves within a resonant tube that is subject to a supersonic air stream. The resonant tube, which may take any one of a number of forms, is located in a nose cone of the projectile that has a nozzle formed at the ogive for directing the fluid flow created while the projectile is in flight onto the open end of the resonant tube. This fluid flow sets up complex cyclical compression waves within the resonant tube which subsequently causes heating of the fluid therein due primarily to the friction within the tube and to the nonisentropic compression of the fluid interacting with the shock waves therein. The heating of the fluid and the high amplitude fluctuations cause a thermoelectric crystal placed near the closed end of the resonant tube to emit an electrical output. The electrical output may be utilized as a power source for any of a number of electrical devices within the projectile.

0 limited States Patent 11 1 1111 3,839,094 Campagnuolo 1 Oct. 1, 19 74FLUIDIC THERMOELECTRIC GENERATOR 3,630,150 12/1971 Rakowsky.... 89/1 B x3,641,346 2/1972 L h b 136213 UX [751 Inventor: Carl Campagnmloh Potomac3,691,408 9 1972 310 4 3,719,532 3/1973 Falkenberg et a1. 310/4Assignee: The United States of America as 3,733,499 5/1973 D618 (it al.l36/2l3 UX represented y the secretary of the 3,736,447 5/1973 Zauderer310/4 Army Washington Primary Examiner-T. H. Tubbesing [22] Filed: June30, 1972 Assistant Examiner-G. E. Montone [211 Appl' No; 267,739Attorney, Agent, or FirmEdward J. Kelly; Saul Elbaum [52] US. Cl136/213, l36/2O5,33ll()/l41, 57 TR C [51] Int Cl H02 1 A thermoelectricgenerator that utilizes the high tem- [58] Field of Search 310/4, 15,11; 102/924, Perame generatedhby 1 cFmpressm waves 1 [02/49] 89/1116/137 R, 259/4 a resonant tube t at is sub ect to a supersonic air136/205 3 21 stream. The resonant tube, which may take any one of anumber of forms, is located in a nose cone of the projectile that has anozzle formed at the ogive for di- [56] References cued recting thefluid flow created while the projectile is in UNITED STATES PATENTSflight onto the open end of the resonant tube. This 783,208 2/1905 K hl1 15/137 R fluid flow sets up complex cyclical compression waves2,666,039 W 1 et a1 l36/213 X within the resonant tube whichsubsequently causes 3,123,739 6/ :964 O Connor 310/4 heating of thefluid therein due primarily to the i 5 3;; 32 7, tion within the tubeand to the non-isentropic com- 340805O 10/1968 zg 25924 pression of thefluid interacting with the shock waves 3711:1125 1111968Marks.IIIIIIIIIIIIIIIIIIII 11111310711 theheih- The heethe ef the hhhdehd the high emph- 3:415 93 2 19 campagnualo et H 102 92 4 tudefluctuations cause a thermoelectric crystal placed 3,467,840 9/1969Weiner 310/4 near the closed end of the resonant tube to emit an3,484,61 1 12/1969 Futaki 136/213 UX electrical output. The electricaloutput may be utilized 3,549,914 12/1970 Jones, Jr. ct a1 310/11 as apower source for any of a number of electrical deg/lllafl'oel et a1vices within the projectile. vans 3,621,310 11/1971 Takeuchi et a1.310/11 8 Clalms, 4 Drawmg Figures FLUIDIC THERMOELECTRIC GENERATORRIGHTS OF GOVERNMENT The invention described herein may be manufactured,used, and licensed by or for the U.S. Government for governmentalpurposes without the payment to me of any royalty thereon.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to flueric generators, and, more particularly, to a fluericgenerator that utilizes a resonant tube in combination with athermoelectric crystal as a power source.

2. Description of the Prior Art In missile and projectile fuzes, it isimportant that an electrical source be provided which will operatereliably for short periods of time. This is normally accomplished byactuating a battery a short time after the missile or projectile hasbecome airborne. Or, perhaps a fluidic-electrical generator is utilizedsuch as disclosed in U.S. Pat. No. 3,555,314. The latter device requiresa multitude of moving parts, such as diaphragms, rods, and springs. Suchmechanical or electromechanical devices are relatively complicated andoften unreliable in their operation due to inherent tendencies to eitherwear out or break down.

It is therefore a primary object of the present invention to provide afluidic means for generating electricity in a missile or projectile thatis devoid of any moving parts.

Another object of the present invention is to provide a thermoelectricgenerator that relies-on the dynamic flow properties of fluid for itsactuation, operation and maintenance.

Another object of the present invention is to provide a thermoelectricgenerator to use in a missile or a projectile that will generateelectricity upon the entrance of ram air into the ogive of theprojectile only after the projectile is a safe distance from thelaunching pad.

A further object of the present invention is to provide a thermoelectricgenerator for use in a missile or projectile that avoids the dependenceupon any externally generated electrical initiation signal by relyingsolely upon the environmental supersonic fluid flow created as theprojectile flies through the air.

SUMMARY OF THE INVENTION A resonant tube closed at one end is adapted toreceive the supersonic flow coming through the ogive of a missile orprojectile. The supersonic flow causes the tube to resonate and heats upits closed end at which is located a thermoelectric crystal. Thecrystal, which may be, for example, bismuth telluride, lead telluride,or barium titanate, emits an electrical output which can be used topower a fuze or trigger a squib. This power can only be available whenthe projectile is in flight, thereby providing an important safetyfeature to the system.

BRIEF DESCRIPTION OF THE DRAWING The specific nature of the invention aswell as other objects, aspects, uses, and advantages thereof willclearly appear from the following descriptions and from the accompanyingdrawings, in which:

FIG. 1 illustrates the combination of a resonant tube and athermoelectric crystal in accordance with the present invention;

FIG. 2 represents another embodiment of a resonant tube and a crystal inaccordance with the present invention;

FIG. 3 represents another preferred embodiment of a resonant tube incombination with a thermoelectric crystal in accordance with theteaching of the present invention; and

FIG. 4 represents still another embodiment of a resonant tube incombination with the crystal of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The embodiment depicted in FIG.1 illustrates a resonant tube 14 with an open end 16 and a closed end 18located adjacent a thermoelectric crystal 10 that has electrical leadsat 12 extending therefrom. The entire resonant tube apparatus of FIG. 1can be located within the ogive of a projectile (not shown) such thatthe ram air received while the missile or projectile is in flight isdirected onto the open end 16 of resonant tube 14 so as to produceinternal resonant oscillations. The crystal 10 is of the thermoelectrictype such as barium titanate, bismuth telluride, or lead telluride, andgenerates an electrical output as a result of the application of heatand/or oscillating high amplitude fluctuations in the resonant tube.

In 1954, Dr. Sprenger in MITTEILUNGEN AUS DEN INSTITUT FUR AERODYNAMIKVol. 21, pages 18 through 34, (AERE LIBRARY TRANSLA- TION 687), taughtthat a resonant cavity, closed at one I end, will become heated at theclosed end when it is stimulated into oscillation by means of a freefluid flow. The resonant cavity becomes heated at its closed end becausethe fluid at the base is compressed with each cycle of oscillation.Shadow graph studies of resonant tubes indicate that shock waves existwithin the tube which are generated by a normal shock in a state ofinstability oscillating between the mouth of the tube and the nozzleexit. When the normal shock is close to the nozzle exit, a compressionwave travels down the tube which becomes steeper due to friction withinthe walls of the tube. The shock impinges at the closed end and isreflected. Upon exiting from the tube, it causes a lower pressure at theentrance. At this time, the normal shock moves across the region ofinstability and causes an expansion wave to be drawn into the tube.After reflection, the expansion wave arrives at the mouth of the tubeand causes the normal shock to move back toward the nozzle. Thus, a newcompression wave is generated and the cycle repeats.

The heating of the fluid is attributed to the friction within the tubeand a non-isentropic compression of the fluid across the shock wave.While a theoretical determination of the temperature in the tube isgreatly complicated by the complex wave distribution, it suffices to saythat extremely small tubes in the order of the 0.2 inches in diametercan be used to produce extremely high temperatures in the range of 600to 1,000F., and these temperatures are sufficient to initiate theoperation of crystal 10 in the device of FIG. 1. It should also be notedthat the temperatures mentioned are generated in fractions of secondsfrom the time the fluid jet impinges upon the resonant tube.

During the operation of the device in FIG. 1, ram air will be directedonto the opening 16 of resonant tube 14, setting the tube 14 intoresonance, thus heating the tube at its closed end 18 due to thecompression waves discussed above. The tube is insulated and thetemperature within rises rapidly. Within approximately half a second,crystal will be stimulated into oscillation to produce electricity alongoutput wires 12. The operation of the thermoelectric crystal 10 of FIG.1 can best be understood by referring to specialized reference texts onthe subject, such as Walshs Energy Conversion, Ronald Press, 1967, Ch.5.

The resonant tube 24 shown in FIG. 2 has been found to produce evenbetter results than the resonant tube 14 used in the embodiment ofFIG. 1. Tube 24 consists of an open end 28 leading to a tube of diameterD. Tube 24 is modified by placing a restrictor 26 of internal diameter dwithin the resonant cavity. The function of the restrictor 26 is to trapsome of the hot gas which would have been carried away from the closedend by the expansion wave discussed above. The position of restrictor 26within the tube 24 is very important and proper placement of therestrictor 26 will maximize the temperature which can be obtained at theclosed end of tube 24 adjacent to crystal 20. Experiments were conductedto demonstrate the temperature at the closed end of the tube 24 forvarious values of L/x, wherein L is the length of the whole resonantcavity and x is the distance between restrictor 26 and the closed end ofthe tube 24. It was discovered that the maximum temperature was producedat the closed end adjacent to crystal 20 when L/x was approximatelyequal to 8. After approximately 4 seconds, the temperature would be inexcess of 600F. The use of this tube in the embodiment shown wouldinsure sufficient temperature to initiate the operation ofthermoelectric crystal 20.

The resonant tube depicted in FIG. 3 is more thoroughly described in mycopending application Ser. No. 238,1 38, filed Mar. 27, 1972, now US.Pat. No. 3,798,475. Resonant tube 34 is seen to consist of a member 36disposed across the center of the open end 39 of cavity 34 in front ofthe entrance to the remainder of the tube. Tube 38 represents anexternal nozzle that provides a supersonic flow of air to the resonanttube 34 and its associated apparatus. As fluid flows out of tube 38, itencounters member 36 and is separated into two halves. Because of thelocation of the entrance to cavity 34 with respect to member 36, part ofthe separated fluid encounters the edges of cavity 34 and thereby flowsinto the cavity. The fluid entering the cavity fills the cavity untilthe pressure within the cavity becomes greater than atmosphericpressure, when fluid leaves the cavity thus lowering the pressure. Whenthe pressure in the cavity becomes lower than atmosphere, the fluidreturns to the cavity and a new cycle initiates. The member 36 whichcreates a fluid instability condition at the open end 39 of cavity 34contributes to the triggering mode of the oscillator. The heat andoscillations thereby generated at the closed end of cavity 34 initiatesthe operation of thermoelectric crystal 30, thus causing an electricaloutput to be fed along wires 32 for the purposes as stated hereinabove.

Another type of resonant tube/oscillator which may be used in the deviceof the present invention is depicted in FIG. 4, which shows a stingoscillator 48 located within a resonant tube 44 adapted to receive ramair from nozzle 38. The operation of the sting oscillator 48 can be bestunderstood with reference to US. Application Ser. No. 47,505 filed June18, 1970. Basically, sting 48, held in place by ribs 50 onto the wallsof a resonant cavity 44, is placed axially or centrally in the path ofthe fluid flow from nozzle 38. As fluid strikes sting 48, high spinfluid vortices are shed by the sting and progress into the cavityexpanding and decreasing their rate of spin, thus converting theirrotational kinetic energy into pressure. The pressure builds up withtranslation of the vortices, thus producing a steepening pressure wave.The pressure wave will reflect off the rear wall of cavity 44 and beexpelled from the opening 46. Thus it is seen that sting 48, by causinginstabilities in the fluid flow, will change the steady state fluidflowing from nozzle 38 into one of periodic pressure pulsation, i.e.,the pressure alternately increases and decreases within cavity 44 withperiodic response as long as an input flow is present at opening 46. Asexplained above, the heating of the resonant tube at its base end nearcrystal 40 will activate the crystal to emit electrical energy alongwires 42.

It is seen that I have provided a thermoelectric generator that haspotential wide application as an electrical energy source in bothmissiles and armed projectiles. The device relies only upon the dynamicsupersonic flow properties of fluids and has no moving parts, thuscontributing to its simplicity, low cost, ruggedness, and long shelflife. It is evident that the heat generated at the base of the resonanttubes described hereinabove could also be transferred at one junction ofa thermopile and the same results obtained as described above. While thethermoelectric generator of my invention has been described in thecontext of this application in ordnance projectiles and missiles, itwill be apparent to those skilled in the art that a wide variety ofother uses are possible. It will be further apparent that theembodiments shown are only exemplary and that various modifications canbe made in construction and arrangement within the scope of theinvention as defined in the appended claims.

I claim as my invention:

1. Apparatus for generating electricity in response to a fluid flow,comprising:

a. a resonant tube having an open end and a closed end;

b. means for directing said fluid flow onto said open end of saidresonant tube to produce fluid compression waves therein;

c. a thermoelectric crystal that generates electrical energy in responseto heat produced at said closed end of said resonant tube by said fluidcompression waves. 7

2. The invention according to claim 1 wherein said resonant tubeincludes a restrictor located on the inner wall of said resonant tubefor retaining within said resonant tube a portion of the heat producedat said closed end, said restrictor having an inner diameter that issmaller than the inner diameter of said resonant tube.

3. The invention according to claim 1 wherein said resonant tubeincludes a rigid rod attached concentrically within said resonant tubeand having a tapered end directed outwardly from said open end of saidresonant cavity for causing perturbations in said fluid flow.

4. The invention according to claim 1 wherein said resonant tubeincludes a member that extends across said open end of said resonantcavity for separating incoming fluid and for converging said fluid atdownsaid fluid flows.

7. The invention according to claim 1 wherein said thermoelectriccrystal is selected from the group consisting of bismuth telluridc, leadtelluridc. and barium titanate.

8. The invention of claim 2 wherein said restrictor is located within aresonant tube of length L at a distance X from said crystal and whereinthe ratio of L/X is 8.

1. APPARATUS FOR GENERATING ELECTRICITY IN RESPONSE TO A FLUID FLOW,COOPRISING: A. A RESONANT TUBE HAVING AN OPEN END AND A CLOSED END; B.MEANS FOR DIRECTING SAID FLUID FLOW ONTO SAID OPEN END OF SAID RESONANTTUBE TO PRRODUCE FLUID COMPRESSION WAVES THEREIN; C. A THERMOSELETRICCRYSTAL THAT GENERATES ELECTRICAL ENERGY IN RESPONSE TO HEAT PRODUCED ATSAID CLOSED END OF SAID RESONANT TUBE BY SAID FLUID COMPRESSION WAVES.2. The invention according to claim 1 wherein said resonant tubeincludes a restrictor located on the inner wall of said resonant tubefor retaining within said resonant tube a portion of the heat producedat said closed end, said restrictor having an inner diameter that issmaller than the inner diameter of said resonant tube.
 3. The inventionaccording to claim 1 wherein said resonant tube includes a rigid rodattached concentrically within said resonant tube and having a taperedend directed outwardly from said open end of said resonant cavity forcausing perturbations in said fluid flow.
 4. The invention according toclaim 1 wherein said resonant tube includes a member that extends acrosssaid open end of said resonant cavity for separating incoming fluid andfor converging said fluid at downstream area, whereby periodicalterations of flow are induced in said resonant cavity.
 5. Theinvention according to claim 4 further including a circular orificemounted upstream of said open end of said cavity.
 6. The inventionaccording to claim 1 wherein said resonant tube comprises asubstantIally conically-shaped body, the tapered end of said body beingthe closed end of said cavity, the open end of said cavity being thebase of said conically-shaped body into which said fluid flows.
 7. Theinvention according to claim 1 wherein said thermoelectric crystal isselected from the group consisting of bismuth telluride, lead telluride,and barium titanate.
 8. The invention of claim 2 wherein said restrictoris located within a resonant tube of length L at a distance X from saidcrystal and wherein the ratio of L/X is 8.